Mud crabs (Scylla spp.) are considered luxury seafood and high market value; hence, mud crab farming is well known in Southeast Asia. However, the prevalence of cannibalistic behavior in crabs thus requires shelter in the culture system to reduce conspecific cannibalism and enhance the survival of crabs. This study aims to determine the suitability of various seaweed species as shelter to improve the survival and production of mud crab Scylla paramamosain crablets. The experiment consisted of seven treatments and was randomly designed in triplicate tanks. The control treatment had no shelter (i.e., without seaweed in the culture tank), and in the other six treatments, red seaweed (Gracilaria tenuistipitata) or green seaweed (Enteromorpha intestinalis) was placed in the rearing tanks at three density levels: 0.5, 1, and 2 kg/m2. Instar 2 crablets were reared at a density of 300 ind/m2, at salinity of 15 g/L, and with continuous aeration. Crablets were fed frozen Artemia biomass to satiation for 4 weeks. Results showed that the survival of crabs in all treatments sharply declined from Week 3 to Week 4 of culture, where the 1 and 2 kg Gracilaria groups showed less reduction than the other treatments. At the end of the experiment, the average survival of crabs in the control group was lowest (17.4%), while the survival of crabs was significantly improved, varying within the ranges of 53.3–70.7% and 27.8–35.9% in the Gracilaria and Enteromorpha groups, respectively. Notably, higher survival resulted in lower growth rates in the seaweed treatments, but enhanced biomass and production of crab juveniles. Moreover, concentrations of TAN, NO2−, NO3−, and PO43− in the Gracilaria treatments were much lower than in both the control and the Enteromorpha treatments that improved water quality in the rearing tanks. The present findings prove that red seaweed G. tenuistipitata could be considered a suitable shelter for the reliable production of mud crab juveniles in the nursery phase.